An ultrasound medical device can be used to treat certain medical conditions. Typically, a portion of the ultrasound medical device is disposed within a subject (e.g., a human), and then the ultrasound medical device is activated so that the portion of the ultrasound medical device disposed within the subject vibrates at an ultrasonic frequency. The ultrasonic vibrations can be used to treat the medical condition (e.g., by ablating tissue in the subject). For example, the ultrasound medical device can be used to treat an occluded region of a blood vessel in a subject by disposing a portion of the ultrasound medical device within the occluded region of the blood vessel and then vibrating the ultrasound medical device at an ultrasonic frequency to ablate the occluded region of the blood vessel.